| Method for the preparation of phytosterols from tall oil pitch -> Monitor Keywords |
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Method for the preparation of phytosterols from tall oil pitchRelated Patent Categories: Chemistry: Natural Resins Or Derivatives; Peptides Or Proteins; Lignins Or Reaction Products Thereof, Lignins Or DerivativesMethod for the preparation of phytosterols from tall oil pitch description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070173639, Method for the preparation of phytosterols from tall oil pitch. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE [0001] This application is a Continuation of prior U.S. patent application Ser. No. 10/964,792, filed Oct. 14, 2004, which is a Continuation of prior U.S. patent application Ser. No. 10/630,572, filed Jul. 30, 2003, which is a Continuation of prior U.S. patent application Ser. No. 09/601,762, filed Aug. 7, 2000, which is a national stage completion (Rule 371) of prior PCT International Application No. PCT/CA99/00150, filed Feb. 19, 1999, which has priority to prior Canadian Patent Application Serial No. 2,230,373, filed Feb. 20, 1998. The benefit of the filing date of each prior application is hereby claimed for all purposes that are legally served by such claim for the benefit of the filing date. FIELD OF THE INVENTION [0002] The present invention relates to a method of preparing phytosterols from tall oil pitch, including the use of distillation techniques to isolate a phytosterol concentrate that can by crystallization yield high purity phytosterols using a solvent comprising alcohol or a combination of alcohols, and that may include water. BACKGROUND TO THE INVENTION [0003] Tall oil pitch is obtained from the black liquor of alkaline digestion of coniferous wood, most notably the kraft process. The black liquor is typically concentrated and settled to yield soap skimmings that contain sodium salts of fatty acids, sodium salts of resin acids and unsaponifiables. The latter group of substances include fatty alcohols, free sterols, steryl esters, and fatty acid esters. In kraft pulp mills, the collected soap is routinely acidulated with a mineral acid such as sulphuric acid to yield an oil phase and a water phase. The oil phase contains free fatty acids, resin acids and unsaponifiables; it is commonly known as crude tall oil. Typically, the amount of unsaponifiables can range from 10 to 35% by weight of the crude tall oil, depending on the species and quality of coniferous wood used. The water phase containing sodium sulphate and any lignin entrained in the original soap is normally recycled back to the pulp mill chemical recovery system. In the subsequent recovery of desired fatty acids and resin acids, crude tall oil is typically evaporated under low pressure conditions to yield a light phase, known as depitched tall oil, containing mainly fatty acids and resins, and a heavy phase, known as tall oil pitch, containing a small amount of fatty and rosin acids and a substantial amount of the original unsaponifiables. [0004] Phytosterols can be isolated from either tall oil soap (sometimes referred to as soap skimmings) or from tall oil pitch. It is understood that the manufacture of sterols from tall oil soap has been practiced commercially by Oy Kaukas AB, Lppeenranta, Finland since 1981. The technologies are those based on the refining of tall oil soap with a combination of low molecular weight ketones, alcohols and hydrocarbons; for example, as disclosed by Holmbom et al. in U.S. Pat. No. 3,965,085 granted on 22 Jun. 1976. The refined tall oil soap is then extracted and crystallized using a combination of polar and non-polar solvents, for example, as taught by Johansson et al. in U.S. Pat. No. 4,044,031 granted on 23 Aug. 1977 and Hamunen in U.S. Pat. No. 4,422,974 granted on 27 Dec. 1983. Those methods of manufacture of pure tall oil sterols requires the soap skimmings to be,relatively free of entrained black liquor and the use of multiple solvents which entails several separate solvent recovery systems. The adjustment of precise solvent compositions to maintain optimal operation for each processing stage is complex. In U.S. Patent No. 4,153,622 granted on 8 May 1979, Lamminkari et al. disclose the use of acetone and activated carbon to extract sterols from tall oil soap, in which the acetone extract is subsequently evaporated for dissolution in ethanol for the final recovery of sterols. [0005] The recovery of sterols from tall oil pitch has been studied for many years. In U.S. Pat. No. 2,715,638, Albrecht et al. teach the use of an amount of dilute alkaline solution to neutralize the fatty and rosin acids in tall oil pitch but in an amount to saponify the sterol ester. The remaining organic phase is then separated and saponified with an alcoholic alkaline solution to convert steryl esters into free sterols for subsequent dilution in hot water to precipitate the sterols by cooling. The product purity was indicated to be in the range of 83%. In U.S. Pat. Nos. 3,691,211 and 3,840,570 Julian teaches the use of a mixture of alcohol, water and hydrocarbon to extract tall oil pitch, then saponify the hydrocarbon phase with an alkali metal base, and finally dissolve the saponified material in a polar solvent for the recovery of phytosterols. The procedure is cumbersome as it involves several solvent extraction steps with different polar and non-polar solvents. The solvent recovery systems for at least polar and non-polar solvents are complex. [0006] In U.S. Pat. No. 5,097,012 granted on 17 Mar. 1992, Thies et al. disclose a method for the isolation of sterols from crude tall oil by water extraction at elevated temperatures and pressures. [0007] In U.S. Pat. No. 3,943,117 granted on 9 Mar. 1976, Force discloses a process for saponifying tall oil pitch in which a water-soluble cationic amine is used in conjunction with an alkali. In U.S. Pat. No. 4,524,024 granted on 18 Jun. 1985, Hughes teaches the hydrolysis of tall oil pitch at elevated temperatures to increase the recovery of fatty acids from tall oil pitch. In U.S. Pat. No.3,887,537 granted on 3 Jun. 1975, Harada et al. disclose the recovery of fatty acids and rosin acids from tall oil pitch by first saponifying tall oil pitch with an alkali metal base and a low molecular weight alcohol, and then introducing the reacted mixture into a thin film evaporator to remove low-boiling matter such as water, alcohol use and light unsaponifiables. The bottom fraction from the first evaporator is next fed to a second thin film evaporator in which the unsaponifiables including sterols are removed as the light ends and a molten soap is recovered as the bottom fraction. Fatty acids and rosin acids are recovered from the molten soap fraction by acidulation conventionally with a mineral acid. In U.S. Pat. No. 3,926,936 granted on 16 Dec. 1975, Lebtinen teaches the recovery of fatty acids and rosin acids from tall oil pitch by reacting tall oil pitch with an alkali at 200 to 300 degrees Celsius, in the amount of 5 to 25% of tall oil pitch, prior to vacuum distillation of the heated mixture to recover the fatty acids and rosin acids in the distillate fraction. [0008] Reference is also made to Chemical abstracts, vol. 112, no. 20, 14 May 1990, Columbus, Ohio US; abstract no. 181758, MALIK, Lubomir et al: "Isolation of phytosterols from tall--oil rosin", XP002104877 & CS 256 092 A (Czech). Malik et al. disclose a process for extracting phytosterols which includes the use of four distillation stages. Product flow is split into parallel distillation paths in a first distillation stage then, following further distillation in each parallel path, is partially recombined prior to a final distillation stage. To achieve high purity phytosterols, the output from the final distillation stage is subjected to two stages of crystallization utilizing relatively large amounts of solvent. SUMMARY OF THE INVENTION [0009] In a broad aspect of the present invention there is provided a new and improved method of preparing phytosterols from tall oil pitch containing steryl esters, the method comprising the steps of: [0010] (a) converting the steryl esters to free phytosterols while in the pitch to produce a modified pitch containing the free phytosterols; [0011] (b) distilling the modified pitch in a first evaporator to remove light ends from the modified pitch and produce a bottom fraction containing the free phytosterols; [0012] (c) distilling only the bottom fraction in a second evaporator to produce a light phase distillate containing the free phytosterols; [0013] (d) distilling only the light phase distillate in a solvent comprising an alcohol to produce a solution containing the free phytosterols; [0014] (e) cooling the solution to produce a slurry with the free phytosterols crystallized in the slurry; and, [0015] (f) washing and filtering the slurry to isolate the crystallized phytosterols. [0016] Preferably, the step of converting the steryl esters to free phytosterols comprises the steps of saponifying the tall oil pitch with an alkali metal base, neutralizing the saponified pitch with an acid, and heating the neutralized pitch to remove water. The resulting pitch with such water removed defines the modified pitch. [0017] Unlike the process of Malik et al., the foregoing process enables the preparation of high purity phytosterol crystals from tall oil pitch with only two distillation stages and only one stage of crystallization, and to do so with the use of a comparatively small amount of solvent. Nevertheless, it may be considered desirable in some cases to achieve phytosterol yields with even higher crystal purity. In accordance with another embodiment of the invention, a marginal improvement is achieved as follows: [0018] (a) producing a light phase distillate containing free phytosterols in the manner described in steps (a) to (c) above; [0019] (b) re-distilling only the light phase distillate so produced to enhance the concentration of free phytosterols in the light phase distillate; [0020] (c) dissolving only the re-distilled light phase distillate in a solvent comprising an alcohol to produce a solution containing the free phytosterols; and, [0021] (d) continuing the procedure as in steps (d) and (f) above to isolate crystallized phytosterols. [0022] Although this procedure involves additional distillation steps, the amount of alcohol required during the crystallization stage remains small compared to the case of Malik et al. BRIEF DESCRIPTION OF THE DRAWINGS [0023] The FIGURE shows a schematic flow diagram for the preparation of high purity phytosterol crystals from tall oil pitch in accordance with the present invention. DESCRIPTION OF PREFERRED EMBODIMENT [0024] In accordance with the present invention, the isolation of phytosterols from tall oil pitch first requires converting steryl esters present in the pitch to free phytosterols while in the pitch. The result is a modified pitch containing free phytosterols. [0025] It is contemplated that the required conversion may be accomplished by various methods. In the FIGURE, the conversion step is indicated by block 30 (shown in broken outline) which receives an incoming feed of tall oil pitch 1 and produces modified pitch 11 as an output. The presently preferred method of conversion involves the use of an alkali base treatment and is indicated by the elements contained within block 30. [0026] As depicted within block 30, tall oil pitch 1 is added with an alkali metal base 2 into a reactor 3. The amount of alkali metal base relative to the tall oil pitch preferably should be sufficient to facilitate substantially complete saponification of the tall oil pitch. [0027] Cost effectiveness considerations will generally favor the use of a water solution of an alkali metal base such as sodium hydroxide, potassium hydroxide or a combination thereof. These compounds or combinations will provide a relatively high alkalinity for a relatively reasonable cost. If such compounds or combinations are used, then the stoichiometric proportion of alkali metal base 2 to tall oil pitch 1 that theoretically is required to achieve complete conversion typically may be in the neighborhood of about 1% by weight. Of course, the precise amount will depend upon the specific characteristics of tall oil pitch 1, and these characteristics may vary from one batch of feed or source to another. As well, and again depending upon the specific characteristics of tall oil pitch 1, it will be recognized that a significant portion of alkali metal base 2 may be consumed by reaction with constituents of pitch 1 other than steryl esters. Accordingly, to provide a strong driving force for the reaction, and to better ensure efficient conversion of the steryl esters that are present, a significantly higher proportion of alkali metal base 2 to tall oil pitch 1 may be considered desirable. Typically, this proportion may be in the range of 5 to 15% by weight. [0028] Mixing is sustained in reactor 3 with sufficient to vigor to maintain contact between pitch 1 and alkali metal base 2. Typically, an operating temperature in the range of 100 to 250 deg. C. for a period in the range of 60 minutes (at the higher temperature) to 300 minutes (at the lower temperature) will suffice to facilitate the desired saponification. 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